The present invention relates generally to a process for the production of electrically conducting organic polymer compounds of polyconjugated structure for use as electrode materials in rechargeable galvanic elements, particularly those which are deposited as films on an electronically conducting surface by anodic current from an aqueous or organic solution of the monomer in the presence of conducting salts.
It has long been known that a variety of polymer compounds which are capable of reversible oxidation and reduction by accepting positive or negative ions of inorganic salts, can be used as chargeable and rechargeable electrode materials in electrochemical cells. To this end, the production of such materials by electropolymerization is especially suitable. In electropolymerization, the polymer is deposited by an anodic current on a suitable carrier from an aqueous or organic solution of the monomer. In the case of a positively doped polymer, to maintain electroneutrality of the polymer during the polymerization, anions of a conducting salt simultaneously present in the solution are also incorporated in the deposition product.
EP-OS No. 166,980 describes the preparation of a conducting polypyrrole, and several pyrrole copolymers, based on this technique. EP-OS No. 99,055 indicates that the above-described electrolysis can be continuously performed by using a rotating roller as the anode. In this case, the roller is only partially submerged in the electrolyte solution, and the deposited active material is continuously removed from the surface of the roller as an endless strip of film.
After the polymer has been incorporated in a galvanic cell, the salt anions incorporated during polymerization can be reversibly removed and added. The rate at which this occurs depends on the thickness of the polymer film. Consequently, a thick film with a correspondingly high capacity may be charged and discharged only with small currents if its charge capacity is to be fully converted.
German patent application No. P 36 07 378.4 describes the use of a polymer foil comprised of several thin film layers instead of a single compact foil of a given thickness. Using such a layered foil as an electrode has been found to allow better utilization of its surface-specific capacity (i.e., better current-carrying capacity with the same charge conversion). However, it remained to provide similar performance in connection with relatively thick, compact films.